You can increase your internal link on main page with the help of Off page SEO tasks like forum posting, article submission, profile submission, and social bookmarking. These are the best SEO techniques for internal link building of main page.

To help better explain the SEO side of this we created an internal link juice tool to show very clearly how much PageRank link juice flows through each link on the site, and then compare that to how much link juice would flow if the number of links were reduced to 100 links. This suddenly turns nebulous talk about best practices into hard numbers that make it much easier to understand the importance of prioritizing what links really deserve a spot in the navigation or the home page.

You should modify your main page content according to your inner pages subject and themes. After that you can use Anchor Tags to keywords that link to your different inner pages. In this way you can increase your internal link on main page. You can also increase inbound links of your website from off page seo activities like article submission, bookmarkings , blog postings, press releases etc..